It is widely known a vehicle power transmission device comprising: (a) a power generation device that includes a rotating machine electrically controllable in torque; and (b) a power distribution device including three rotating elements, which are an input rotating element, a first output rotating element operatively coupled to a first wheel, and a second output rotating element operatively coupled to a second wheel, the power distribution device distributing power input to the input rotating element from the power generation device to the first output rotating element and the second output rotating element. One example is a vehicle power transmission device described in Patent Document 1, and the vehicle power transmission device is related to a hybrid drive type front and rear wheel drive vehicle and is equipped with the power generation device having (a-1) an electric type differential portion with the rotating machine (motor generator) coupled to a differential mechanism in a power transmittable manner to control a differential state between a rotation speed of a differential input member and a rotation speed of a differential output member by controlling the operation state of the rotating machine and (a-2) a power source (engine) coupled to the differential input member in a power transmittable manner.
One example is a power transmission device 100 of a hybrid vehicle having a general configuration (schematic) depicted in FIG. 19, which includes a power generation device 101 and a front and rear wheel power distribution device 104. The power generation device 101 includes an engine 110 used as a main power source and an electric type differential portion 102, and the electric type differential portion 102 includes a single pinion type differential planetary gear device 106 as a differential mechanism. A carrier SCA of the differential planetary gear device 106 is coupled via a differential input shaft 108 etc., as a differential input member to the engine 110; a sun gear SS is coupled to a first motor generator MG1 as a rotating machine; a ring gear SR is integrally coupled to a differential output member 112. The front and rear wheel power distribution device 104 is made up mainly of a double pinion type distribution planetary gear device 114, and a ring gear CR of the distribution planetary gear device 114 is an input rotating element and is integrally coupled to the differential output member 112. A sun gear CS is a first output rotating element and is operatively coupled to a rear wheel (first wheel) via a rear-wheel output shaft 116 etc., and a carrier CCA is a second output rotating element and is operatively coupled to a front wheel (second wheel) via a front-wheel output gear 118 etc. The rear-wheel output shaft 116 is coupled to a second motor generator MG2 as a sub-power source in a power transmittable manner.
As depicted in a collinear diagram of FIG. 20 capable of representing the rotation speeds of the portions of the electric type differential portion 102 with a straight line, the power transmission device 100 as described above controls an engine rotation speed NE, i.e., the rotation speed of the differential input shaft 108 in consideration of fuel economy etc., and the first motor generator MG1 is subjected to the regenerative control so as to achieve a predetermined rotation speed NMG1 determined depending on the rotation speed of the differential output member 112. i.e., vehicle speed V. The power running control of the second motor generator MG2 is performed with the electric energy acquired from the regenerative control of the first motor generator MG1 to add an assist torque to the rear wheel side, and an engine load is correspondingly reduced. A ratio of intervals among the rotating elements (SS, SCA, SR) in the collinear diagram of FIG. 20 is determined depending on a gear ratio (=number of teeth of sun gear/number of teeth of ring gear) ρS of the differential planetary gear device 106. FIG. 20 also depicts a collinear diagram related to the front and rear wheel power distribution device 104; “Rr” is the rotation speed of the rear-wheel output shaft 116, i.e., the rotation speed of the sun gear CS; “Fr” is the rotation speed of the front-wheel output gear 118, i.e., the rotation speed of the carrier CCA; and this example represents the case that the gear ratio from the rear-wheel output shaft 116 to the rear wheel is the same as the gear ratio from the front-wheel output gear 118 to the front wheel and that the rotation speeds thereof are equivalent to each other. For the front and rear wheel power distribution device 104, a ratio of intervals among three rotating elements including the ring gear CR is determined depending on a gear ratio ρC of the distribution planetary gear device 114.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-114944